The present invention relates to a method for loop communication, and more particularly to a communication method for operating a plurality of loop communication paths as a composite loop communication network.
In the prior art, a plurality of loop communication paths are combined with one another, for example, by a method disclosed in Japanese patent application Unexamined Publication No. 58-116837. In this method, a plurality of loop communication paths are combined with one another through a loop coupling device, and the loop coupling device takes in a frame (namely, the transmission unit of data) whose destination loop is different from the sending loop of the frame, to send the frame to the destination loop. Further, in a case where the communication between the loop coupling device and the destination loop is made impossible by a fault, or the destination loop is in a busy condition, the loop coupling device informs a terminal which has made a call request, that the communication with the destination loop is impossible.
As mentioned above, in the conventional method, a plurality of loop communication paths are combined with one another so that the communication between terminals of different loops is made without taking the routing control into consideration. That is, attention is not paid to the routing control that, when a plurality of communication routes exist between two terminals, an optimum route is selected by taking into consideration a busy condition and the position of a fault. Further, in the conventional method, a plurality of loop communication paths are combined with one another through only one loop coupling device, and hence no attention is paid to a system in which a plurality of loop communication paths are combined with one another through a plurality of loop coupling devices so as to operate as a loop communication network, and an optimum one of a plurality of possible communication routes between two terminals can be dynamically determined by taking into consideration the busy condition and the presence of any fault in the communication routes.
In a case where such a loop communication network (that is, a composite loop system) is formed by combining a plurality of loop communication paths organically, it is an important problem how efficiently the routing control is carried out for the communication between two terminals which are connected to different loops.